Lensless vision system for in-plane positioning of a patterned plate with subpixel resolution.

Whereas vision is an efficient way for noncontact sensing of many physical quantities, it assumes a cumbersome imaging system that may be very problematic in confined environments. In such contexts, the design of a compact vision probe can be based on digital holography that is a lensless imaging principle. In this interferometric method, object scenes are reconstructed numerically through wave propagation computations applied to a diffracted optical field recorded as an interferogram. We applied this approach to the visual positioning of a micropatterned glass plate. The pseudoperiodic pattern deposited on the surface is suited for absolute in-plane position determination as well as for fine object-feature interpolation leading to subpixel resolution. Results obtained demonstrate a lateral resolution of 0.1 μm, corresponding to 1/20th of a pixel, from a 150 μm period of the pseudoperiodic pattern and with a demonstrated excursion range of 1.6 cm. In the future, such position encoding could be applied to the backside of standardized sample holders for the easy localization of regions of interest when specimens are transferred from an instrument to another one, for instance in nanotechnology processes.